Process for preparation of a nitrophenol

ABSTRACT

The invention relates to a method of preparing a high-purity nitrophenol and, more specifically, p-nitrophenol from a nitrohalobenzene. The inventive method comprises the following steps: (a) hydrolysis of a nitrohalobenzene compound by reacting said compound with a base; (b) acidification in order to produce the nitrophenol compound from the salt thereof by means of an acid treatment; (c) crystallisation of the nitrophenol compound obtained; and (d) separation of the product obtained. The invention is characterised in that it also comprises at least the following steps: (e) concentration of the reaction medium after hydrolysis (a) and before acidification (b); and (f) liquid/liquid decantation after acidification (b) and before crystallisation (c), which is intended to eliminate the water phase obtained after acidification (b).

The object of the present invention is a process for preparation of anitrophenol of high purity.

More precisely, the invention aims to provide a nitrophenol free fromits halogen-containing impurities in inorganic or organic form.

More particularly, the invention concerns a process for preparation ofp-nitrophenol.

p-Nitrophenol is an intermediate compound used in the plant protectionfield, in particular in the preparation of insecticides.

It is also used in the pharmaceutical field, mainly as an intermediatefor the production of APAP, namely N-acetyl-p-aminophenol.

For this purpose, the p-nitrophenol must satisfy rather stringent purityrequirements.

One of the routes for preparation of p-nitrophenol consists inperforming a basic hydrolysis of p-nitrochlorobenzene, most oftenperformed with the use of a solution of sodium hydroxide, thenacidification of the sodium phenate salt formed, generally with sulfuricacid.

The problem which arises is that the said process does not result in ap-nitrophenol of high purity, in particular on account of the presenceof chlorine, present either in inorganic form, for example owing to theresidual presence of p-nitrochlorobenzene, or in organic form (chlorideions), for example owing to the residual presence of sodium chloridewhich results from the reaction of the p-nitrochlorobenzene and thesodium hydroxide but also on account of the presence of various coloredby-products, in particular azo or azoxy species.

In order to mask the formation of colored products, it has been proposedto perform the basic hydrolysis either in the presence of a peroxide (DE1543952) or by introducing an oxygen-containing gas (U.S. Pat. No.3,283,011).

Moreover, according to U.S. Pat. No. 3,624,164, a process forpreparation of salts of nitrophenols has been described. It consists inperforming a basic hydrolysis of p-nitrochlorobenzene followed byconcentration of the medium, and crystallization of the correspondingphenate. In addition, the obtention of p-nitrophenol by acidification,followed either by recovery of a liquid p-nitrophenol phase byseparation of the aqueous phase, or by recovery of the solid phenol bycrystallization of the reaction medium. However, the p-nitrophenolobtained does not meet the desired purity criteria as regards chlorinecontent.

The objective of the invention is to propose a versatile process whichmakes it possible to control the purity of the nitrophenol required andto obtain a product meeting the requirements of high purity.

Thus, depending on the choice of steps, it is possible to adjust thepurity of the product obtained.

A process has now been found, and it is this that comprises the objectof the present invention, for preparation of a nitrophenol from anitrohalobenzene which consists in performing:

-   -   (a) hydrolysis of a nitrohalobenzene compound by reaction of the        said compound with a base,    -   (b) acidification to obtain the nitrophenol compound from its        salt, by an acid treatment,    -   (c) crystallization of the nitrophenol compound obtained,    -   (d) separation of the product obtained,        characterized in that it also includes at least the following        steps:    -   (e) concentration of the reaction medium after hydrolysis (a)        and before acidific-ation (b),    -   (f) liquid/liquid decantation performed after acidification (b)        and before crystalliz-ation (c) and intended to remove the        aqueous phase obtained after acidification (b).

More precisely, the process comprises the following steps, namely:

-   -   (a) hydrolysis of a nitrohalobenzene compound by reaction of the        said compound with a base,    -   (e) concentration of the reaction medium,    -   (b) acidification to obtain the nitrophenol compound from its        salt, by an acid treatment,    -   (f) liquid/liquid decantation intended to remove the aqueous        phase obtained after acidification (b).    -   (c) crystallization of the nitrophenol compound obtained,    -   (d) separation of the product obtained.

Thus, according to the invention a nitrophenol is obtained which has alow content of liposoluble impurities (nitrohalobenzenes, for examplep-nitrochlorobenzene (PNCB), nitrobenzene (typical impurity of thenitrohalobenzenes) which is shown by:

-   -   a nitrohalobenzene (in particular p-nitrochlorobenzene) content        less than 180 ppm, preferably less than 50 ppm.

According to the invention, a nitrophenol also freed from impuritiessoluble in water (sodium chloride, sodium sulfate, hydrophilic organicssuch as organic sulfonates or sulfates) is obtained, which is shown by:

-   -   a halide ions content less than 40 ppm, preferably less than 20        ppm,    -   a sulfur content preferably less than 200 ppm and still more        preferably less 100 ppm.

Thus, the process of the invention also makes it possible to provide anitrophenol freed from its sulfurous impurities which are present whensulfuric acid is used in the process of the invention as the agent foracidification of the nitrophenol formed intermediately.

The process makes it possible substantially to decrease the sulfurcontent which is particularly advantageous on account of the intendeduse of the nitrophenol. In fact, given the fact that the nitro group isreduced to an amino group by catalytic hydrogenation in the course of asubsequent step in order to obtain the APAP, it is desirable that thecatalyst contain little residual sulfur, as sulfur is a well-knowncatalyst poison.

Another typical solution would consist in increasing the number ofnitrophenol crystallization operations. However, this alternative is notadvantageous in terms of yield and product loss.

According to the process of the invention, which simultaneously combinesa concentration and a decantation step, a product which is purer as ithas been freed of two types of impurity is obtained.

According to another modification of the invention, an intermediateseparation of the nitrophenate obtained following the basic hydrolysisis performed, which makes it possible to obtain a nitrophenol having astill higher degree of purity.

The purity is further improved according to another modification whichconsists in performing a water washing of the organic phase recoveredfollowing the decantation.

A nitrohalobenzene (NHB) is involved in the process of the invention,which can be represented by the following general formula:

In the said formula (I), X represents a fluorine, chlorine, bromine oriodine atom, preferably a chlorine atom,

In the formula (I), the NO₂ group is in the ortho, meta or para positionand preferably in the para position.

The present invention does not exclude the presence of othersubstituents on the aromatic ring provided that do not interfere withthe reactions of the process of the invention. In particular, it ispossible that one or several other atom(s) of halogen or of one orseveral nitro group(s) or of one or several alkyl group(s) having from 1to 4 carbon atoms may be present.

Several is understood to mean at most 4 substituents. More particularly,the invention concerns the nitromonohalobenzenes, preferably o-, m- orp-nitrochlorobenzene.

Use may also be made of the product available on the market which ispreferably of purity greater than 99%.

In order to facilitate understanding of the process of the invention,FIGS. 1 to 3 are given below, which present in diagrammatic form thedifferent modifications of the process of the invention, without howeverrestricting the scope of the invention to these.

FIG. 1

According to the process of the invention, firstly the basic hydrolysisof the nitrohalobenzene is performed by reacting it with an inorganic ororganic base.

A strong base, that is to say a base having a pKb greater than 12, ispreferably chosen, the pKb being defined as the cologarithm of thedissociation of the base, measured in an aqueous medium at 25° C.

Particularly well suited for the implementation of the process of theinvention are inorganic bases such as the salts of alkali metals,preferably an alkali metal hydroxide, which can be sodium, cesium,rubidium or potassium hydroxide.

It is possible to use a trialkylammonium hydroxide, but this does notpresent any additional advantage.

For economic reasons, among all the bases, sodium or potassium hydroxideare preferably chosen.

The concentration of the starting basic solution is not critical. Thealkali metal hydroxide solution used is generally of concentration lyingbetween 5 and 70% by weight, preferably 7 to 50%.

The quantity of base introduced into the reaction medium takes accountof the quantity necessary to hydrolyze the halogen atom of the startingnitrohalobenzene compound.

Generally, for almost complete or complete conversion of thenitrohalobenzene, the quantity of base expressed by the ratio betweenthe number of moles of base and the number of mole of nitrohalobenzeneis at least 2 and preferably lies between 2 and 3. It can however ifnecessary be less than 2 or greater than 3.

Water is present in the medium, in a quantity such that thenitrohalobenzene represents, in weight percent relative to the totalityof the mass of the reaction medium, 1% to 50% and preferably from 7% to25%.

The process of the invention is advantageously conducted at atemperature lying between 100° C. and 200° C., preferably between 140°C. and 180° C.

The process is preferably conducted under the self-generated pressure ofthe reactants.

The duration of this hydrolysis step is variable. As an indication, itis stated that it most often takes between 1 and 6 hours. The durationof this step must quite obviously be linked to the other parameters, inparticular the temperature.

From a practical point of view, the reactants, nitrohalobenzene andbase, can be loaded into an autoclave and then heated. It is alsopossible to load the reactants consecutively, in particular the sodiumhydroxide and then to add the nitrohalobenzene in portions or run it in.

At the end of the hydrolysis reaction, the nitrophenol is obtained inthe form of a salt, the associated cation deriving from the base used.Hereinafter it is referred to as “nitrophenate”.

According to one characteristic of the process of the invention,concentration of the reaction medium can be performed so as to increasethe concentration of the nitrophenate in the medium from 0.1% by weightto 10% by weight, preferably from 0.5% to 3%.

Thus, in the course of this operation, a fraction (F₁) comprising water(for example from 1 to 20 weight % relative to the mass of the reactionmedium coming from the hydrolysis), the starting reactantnitrohalobenzene that has not reacted and all the volatile compoundsthat can be entrained in steam or can form an azeotrope with water, suchas for example nitrobenzene, is eliminated.

By means of this step, the purity of the final product is improvedconsiderably, particularly when the hydrolysis medium contains organicmaterials of low solubility in water.

A first mode consists simply in decreasing the reaction pressure, bypressure release, while remaining in the aforesaid temperature range.This pressure release is effected in such a manner as to remove at thehead the quantity of water necessary to attain the target concentrationof nitrophenate in the reaction medium.

By elimination of water and volatile impurities, the desiredconcentration of nitrophenol, obtained in salt form, is obtained.

Another mode of implementation for concentration of the reaction mediumconsists in performing the distillation of the quantity of part of thewater to attain the desired concentration of nitrophenol, obtained insalt form, in the reaction medium.

The distillation can be performed at atmospheric pressure at atemperature of the order of 100° C.

The distillation can also be performed under a pressure slightly lowerthan atmospheric pressure, for example from 20 to 750 mm of mercury andat a temperature lower than 100° C. In general, the pressure is chosenso as to have a distillation temperature lying between 80° C. and 99.6°C.

The distillation can also be performed under a pressure greater thanatmospheric pressure.

Another mode consists in performing an entrainment by injection of afluid, for example steam or inert gas, in particular nitrogen.

According to the process of the invention, the acidification of thenitrophenate obtained is performed in a following step in order togenerate the hydroxyl group.

For this purpose, the product obtained is firstly brought into aqueoussolution or suspension. The quantity of water that may be added is suchthat the concentration of nitrophenate varies from 10 to 80%, preferablyfrom 15 to 50%.

This operation is performed at a temperature varying between 30° C. and80° C., preferably between 50° C. and 60° C.

In a following step, the reaction medium is acidified by addition of aprotonic acid of inorganic origin, preferably hydrochloric acid orsulfuric acid.

Use is preferably made of a concentrated solution of sulfuric acid ofconcentration greater than 95% by weight, preferably from 96 to 98%.

The quantity of acid is at least equal to the quantity necessary toneutralize the nitrophenate. Generally, it is such that at the end ofacidification a pH lying between 1 and 7, preferably between 2 and 5, isobtained.

The reaction medium is maintained at a temperature varying for examplebetween 45° C. and 70° C., and preferably from 50° C. to 60° C.

The process is preferably conducted under the atmospheric pressure ofthe reactants.

A two-phase medium is obtained, consisting of a liquid phase comprisinga water/nitrophenol mixture essentially containing the nitrophenol(about 70% in the case of p-nitrophenol) and an aqueous phase comprisingthe excess acid, preferably sulfuric acid, the salts obtained followingthe acidification, most commonly sodium sulfate and possibly, and inminor amounts, water-soluble organic products, which may for exampleresult from the sulfonation of the benzene nucleus.

According to a preferred modification of the process of the invention,an operation of decantation of the two liquid phases obtained isperformed following the acidification, in the range of temperaturesstated above for the acidification, preferably 60-70° C.

A separation of the aqueous phase (F₄) comprising the excess sulfuricacid, the salts obtained following the acidification, most commonlysodium sulfate and, in minor amounts, products resulting from thesulfonation of the benzene nucleus of the organic phase comprisingessentially nitrophenol, is performed.

Part of this aqueous phase can advantageously be recycled to thehydrolysis or the acidification step.

Generally, for example from 10 to 50% of this phase (%) by weight can berecycled.

The solid, essentially consisting of nitrophenol, which precipitatesduring the cooling of (F₄), can also be recycled to the same steps.

From the organic phase, the crystallization of the nitrophenol iseffected by cooling to a temperature which is a temperature lower than40° C., preferably the ambient temperature or even lower.

During this step, the concentration of the nitrophenol can vary from 10to 70%, preferably from 20 to 60%.

The separation of the crystallized product is then performed by thestandard solid/liquid separation techniques, preferably by filtration orby centrifugation.

The separation is conducted at the temperature of the end ofcrystallization.

A solid which is essentially the nitrophenol (NP) and an aqueous phase,consisting of the crystallization mother liquors and washing liquors(F₃) containing nitrophenol at the limit of its solubility and salineresidues are recovered.

It should be noted that the aqueous phase is of low salinity and canadvantageously be recycled to the hydrolysis or phenate acidificationstep.

One or several washings of the nitrophenol obtained with water can ifnecessary be effected.

A nitrophenol containing less than 50 ppm of halonitrobenzene but whichcontains less than 100 ppm of halide and less than 100 ppm of sulfur isrecovered.

FIG. 2

According to the process of the invention, firstly the basic hydrolysisof the nitrohalobenzene compound is performed as described above and atthe end of the reaction the nitrophenol is obtained in salt form.

According to one characteristic of the process of the invention,concentration of the reaction medium can be performed so as to increasethe concentration of the nitrophenol in the medium from 0.1% by weightto 10% by weight, preferably from 0.5% to 3%.

Thus, in the course of this operation, a fraction (F₁) comprising water(for example from 1 to 10% weight relative to the mass of the reactionmedium coming from the hydrolysis), the starting reactantnitrohalobenzene that has not reacted and all the volatile compoundsthat can be entrained in steam or can form an azeotrope with water, suchas for example nitrobenzene is eliminated.

By means of this step, the desired concentration is obtained and purityof the final product is improved considerably, particularly when thehydrolysis medium contains organic materials of low solubility in water.

To carry out the concentration, the modes of implementation describedfor FIG. 1 are used.

At the end of this operation, the crystallization of the nitrophenateobtained is performed, by cooling to a temperature which is the ambienttemperature (most commonly lying between 15° C. and 25° C.)

The separation of the crystallized product can next be performed by thestandard solid/liquid separation techniques, preferably by filtration orcentrifugation. The separation is typically conducted at a temperaturelying between 0° C. and 200° C.

A solid which is essentially the nitrophenate and an aqueous phase (F₂)containing the salts generated by the hydrolysis reaction, essentiallysodium chloride and a dissolved nitrophenate fraction is recovered.

One or several, for example up to 3, washings can if necessary beperformed with water or water saturated with sodium hydroxide or sodiumchloride.

According to the process of the invention, the acidification of thenitrophenate obtained is performed in a following step in order togenerate the hydroxyl function, which is performed under the conditionsdescribed in FIG. 1.

A two-phase medium is obtained, consisting of a liquid phase comprisinga water/nitrophenol mixture essentially containing the nitrophenol(about 70% in the case of p-nitrophenol) and an aqueous phase comprisingthe excess acid, preferably sulfuric acid, the salts obtained followingthe acidification, most commonly sodium sulfate and possibly, and inminor amounts, water-soluble organic products, which may for exampleresult from the sulfonation of the benzene nucleus.

According to a preferred modification of the process of the invention,an operation of decantation of the two liquid phases obtained isperformed following the acidification, in the range of temperaturesstated above for the acidification, preferably 60-70° C.

A separation of the aqueous phase (F₄) comprising the excess sulfuricacid, the salts obtained following the acidification, most commonlysodium sulfate and, in minor amounts, products resulting from thesulfonation of the benzene nucleus of the organic phase comprisingessentially nitrophenol, is performed.

Part of this aqueous phase can advantageously be recycled to thehydrolysis or the acidification step. Generally, for example from 10 to50% of this phase (%) by weight can be recycled.

The solid, essentially consisting of nitrophenol, which precipitatesduring the cooling of (F₄), can also be recycled to the same steps.

From the organic phase, the crystallization of the nitrophenol iseffected by cooling to a temperature which is a temperature lower than40° C., preferably the ambient temperature or even lower.

During this step, the concentration of the nitrophenol can vary from 10to 70%, preferably from 20 to 60%.

The separation of the crystallized product is then performed by thestandard solid/liquid separation techniques, preferably by filtration orby centrifugation.

The separation is conducted at a temperature lying between 0° C. and 20°C.

A solid which is essentially the nitrophenol (NP) and an aqueous phase(F₃) containing nitrophenol at the limit of its solubility and salineresidues are recovered.

It should be noted that the aqueous phase is of low salinity and canadvantageously be recycled to the nitrophenate aqueous dissolution orsuspension step, or indeed also to the hydrolysis.

One or several washings of the nitrophenol obtained with water can ifnecessary be effected.

A nitrophenol containing less than 50 ppm of halonitrobenzene and lessthan 50 ppm of halide and less than 100 ppm of sulfur is recovered.

FIG. 3

According to the process of the invention, firstly the basic hydrolysisof the nitrohalobenzene compound is performed as described above and atthe end of the reaction the nitrophenol is obtained in salt form.

According to one characteristic of the process of the invention,concentration of the reaction medium can be performed so as to increasethe concentration of the nitrophenol in the medium from 0.1% by weightto 10% by weight, preferably from 0.5% to 3%.

Thus, in the course of this operation, a fraction (F₁) comprising water(for example from 1 to 10% weight relative to the mass of the reactionmedium coming from the hydrolysis), the starting reactantnitrohalobenzene that has not reacted and all the volatile compoundsthat can be entrained in steam or can form an azeotrope with water, suchas for example nitrobenzene is eliminated.

By means of this step, the desired concentration is obtained and purityof the final product is improved considerably, particularly when thehydrolysis medium contains organic materials of low solubility in water.

To carry out the concentration, the modes of implementation describedfor FIG. 1 are used.

According to a first modification, the acidification of the nitrophenateobtained is performed in the following step.

According to another modification, crystallization and separation of thenitrophenate obtained is performed immediately before the acidification.

Thus, at the end of the concentration operation, the crystallization ofthe nitrophenate obtained is performed, by cooling to a temperaturewhich is the ambient temperature (most commonly lying between 15° C. and25° C.).

The separation of the crystallized product can next be performed by thestandard solid/liquid separation techniques, preferably by filtration orcentrifugation. The separation is typically conducted at a temperaturelying between 0° C. and 20° C.

A solid which is essentially the nitrophenate and an aqueous phase (F₂)containing the salts generated by the hydrolysis reaction, essentiallysodium chloride and a dissolved nitrophenate fraction is recovered.

One or several, for example up to 3, washings can if necessary beperformed with water or water saturated with sodium hydroxide or sodiumchloride.

According to the process of the invention, the acidification of thenitrophenate obtained is performed in a following step in order togenerate the hydroxyl function, which is performed under the conditionsdescribed in FIG. 1.

A two-phase medium is obtained, consisting of a liquid phase comprisinga water/nitrophenol mixture essentially containing the nitrophenol(about 70% in the case of p-nitrophenol) and an aqueous phase comprisingthe excess acid, preferably sulfuric acid, the salts obtained followingthe acidification, most commonly sodium sulfate and possibly, and inminor amounts, water-soluble organic products, which may for exampleresult from the sulfonation of the benzene nucleus.

According to a preferred modification of the process of the invention,an operation of decantation of the two liquid phases obtained isperformed following the acidification, in the range of temperaturesstated above for the acidification, preferably 60-70° C.

A separation of the aqueous phase (F₄) comprising the excess sulfuricacid, the salts obtained following the acidification, most commonlysodium sulfate and, in minor amounts, products resulting from thesulfonation of the benzene nucleus of the organic phase comprisingessentially nitrophenol, is performed.

Part of this aqueous phase can advantageously be recycled to thehydrolysis or the acidification step. Generally, for example from 10 to50% of this phase (%) by weight can be recycled.

The solid, essentially consisting of nitrophenol, which precipitatesduring the cooling of (F₄), can also be recycled to the same steps.

In one modification, a step of washing the organic phase is interposedbetween the decantation and the crystallization.

The quantity of water necessary for this step can vary in largeproportions.

By way of indication, it may be stated that the water can be used in aquantity such that there is 0.1 to 2 kg of water per kg of organicphase, preferably from 0.2 to 1 kg of water per kg of organic phase.

Part of the fraction (F₃) derived from a previous production run can beused for this washing step. It should be noted that these new aqueouswashings (F₅), which are of low salinity, can advantageously be recycledto the nitrophenate aqueous dissolution or suspension step, or indeedalso to the hydrolysis.

From the organic phase, the crystallization of the nitrophenol iseffected by cooling to a temperature which is a temperature lower than40° C., preferably the ambient temperature or even lower.

During this step, the concentration of the nitrophenol can vary from 10to 70%, preferably from 20 to 60%.

The separation of the crystallized product is then performed by thestandard solid/liquid separation techniques, preferably by filtration orby centrifugation.

The separation is conducted at a temperature lying between 0° C. and 20°C.

A solid which is essentially the nitrophenol (NP) and an aqueous phase(F₃) containing nitrophenol at the limit of its solubility and salineresidues are recovered.

It should be noted that the aqueous phase is of low salinity and canadvantageously be recycled to the nitrophenate aqueous dissolution orsuspension step, or indeed also to the hydrolysis.

One or several washings of the nitrophenol obtained with water can ifnecessary be effected.

A nitrophenol containing less than 50 ppm of halonitrobenzene and lessthan 20 ppm of halide and less than 100 ppm of sulfur is recovered.

Following the different steps constituting the object of the process ofthe invention, for example according to the process represented by FIG.1, a product satisfying all the purity criteria stated at the beginningof the present text is obtained, and according to the processes of FIGS.2 and 3 a product which can be purer.

Examples of the implementation of the invention are given below.

EXAMPLES

Before describing the examples in detail, an example is given of thehydrolysis of paranitrochlorobenzene as in the state of the technology.

The synthesis of sodium paranitrophenate (referred to below as phenate)is effected under standard conditions, already previously described (seefor example U.S. Pat. No. 3,283,011).

In particular, the reaction masses of hydrolysate, the starting materialfor our purification sequences, are obtained by heating a reactionmixture consisting of: PNCB (paranitrochlorobenzene) 1294.5 g (8.2moles) sodium hydroxide 694.4 g (17.4 moles) water 4500 g for 2 hours inan autoclave at 170° C. (under self-generated pressure of 7-7.2 bars)

After cooling to ambient temperature, the medium is filtered, resultingin a moist solid and mother liquors.

The outcome of the experiment is summarized below. Thep-nitrochlorobenzene is estimated by high performance liquidchromatography (HPLC). The total chlorine and the sulfur are estimatedby Xray fluorescence. The chlorides are estimated by argentimetrictitration. The OD (optical density) at 500 nm expresses the colorationof the product, measured by UV/visible spectrometry. NaPNP Mass (g)(moles)* Yield Moist solid 2773 7.87** S Mother 3714 0.11 liquors MLTotal 6487 7.98 97.3%- HPLC estimation;**45.3% of phenate expressed as non-hydrated form.

Example 1

In this example, the p-nitrophenol is prepared by a process utilizing aconcentration step and a decantation step.

This example is conducted according to FIG. 1.

352 g of moist solid (S) and 774 g of mother liquors (ML), namely 1.02moles of phenate, are introduced into a 2 liter multineck flask fittedwith a central stirrer (500 rpm) and heated by a double jacket.

The reaction medium is distilled so as to eliminate 74 g of water, underatmospheric pressure.

The reaction medium is brought back to 60° C.

The phenate is then neutralized by acidifying the medium by addition of56.2 g of concentrated sulfuric acid (96%).

The duration of the addition is 1 hr 30 and the final pH is 3.

At the end of the acidification of the phenate, the aqueous phase (540g) is removed by decantation.

610 g of water is added to the aqueous phase.

The mixture is cooled to 15° C.

The p-nitrophenol crystallizes.

The solid obtained is filtered.

It is washed with 150 g of deionized water.

After drying, 127 g of dry solid, titrating as 98.5% p-nitrophenol (PNP)(0.904 moles) is obtained.

The analytical results are presented in the summary table (I).

Example 2 Effect of Concentration, Crystallization of the Phenate andDecantation

This example is conducted according to FIG. 2.

Example 1 is reproduced, but with the addition of a phenatecrystallization step between the concentration step and the phenateacidification step.

After the removal of water to concentrate the medium, it is cooled to15° C. and the phenate that precipitates is recovered by filtration.

A washing is performed using 160 g of a 13.5% by weight aqueous solutionof sodium chloride.

The moist phenate is resuspended in 370 g of water, this is brought upto 60° C., and the phenate is then neutralized by acidifying the mediumby addition of 56.5 g of concentrated sulfuric acid (96%).

The decantation is performed at 60° C. and the mixture is cooled to 15°C. to effect the crystallization of the p-nitrophenol and drying isperformed as in Example 1.

125.9 g of dry solid, titrating as 99% PNP (0.896 moles), are recovered.

The analytical results are presented in the summary table (I).

Example 3 Effect of Concentration, Crystallization of the Phenate,Decantation and Washing of the Organic Phase

This example is conducted according to FIG. 3.

Example 2 is repeated, with the addition of a step of aqueous washing ofthe decanted organic phase (washing water: 160 g).

124.4 g of dry solid, titrating as more than 99.5% PNP (0.89 moles), arerecovered.

The analytical results are presented in the summary table (I).

Comparison Example 1

In this example, the p-nitrophenol is prepared by a process usingneither a concentration step, nor a decantation step.

352 g of moist solid (S) and 774 g of mother liquors (ML), namely 1.02moles of phenate, are introduced into a 2 liter multineck flask fittedwith a central stirrer (500 rpm) and heated by a double jacket.

The reaction medium is brought up to 60° C.

The phenate is then neutralized by acidifying the medium by addition of56.2 g of concentrated sulfuric acid (96%).

The duration of the addition is 1 hr 30 and the final pH is 3.

The mixture is cooled to 15° C.

The solid obtained is filtered.

It is washed with 132 g of deionized water.

After drying, 140.4 g of dry solid (drying under vacuum for 15 hours at60° C.), titrating as 96% PNP (0.969 moles) are recovered.

The analytical results are presented in the summary table (I).

Comparison Example 2 This Example is Conducted with Omission of theDecantation Step

This example is conducted according to Comparison Example 1 but aconcentration step is added between the hydrolysis step and theacidification.

At the end of the hydrolysis, the reaction medium is distilled so as toeliminate 74 g of water.

The analytical results are presented in the summary table (I).

Comparison Example 3 This Example is Conducted with Omission of theConcentration Step

This example is conducted according to Comparison Example 1 but adecantation step is added between the acidification of the phenate andthe crystallization of the p-nitrophenol.

126 g of dry solid, titrating as 98.4% PNP (0.89 moles), are recovered.

The analytical results are presented in the summary table (I).

Comparison Example 4

This example is conducted according to Example 2 but with omission ofthe decantation step which follows the acidification of the phenate.

Following the acidification, the mixture is cooled to 15° C. to effectthe crystallization of the p-nitrophenol, and drying is performed as inExample 1.

135.5 g of dry solid, titrating as 96% PNP (0.935 moles), are recovered.

The analytical results are presented in the summary table (I). TABLE IComparison Comparison Comparison Comparison Ex. 1 Ex. 2 Ex. 3 Ex. 1 Ex.2 Ex. 3 Ex. 4 Concentration Yes Yes Yes No Yes No Yes Crystallization NoYes Yes No No No Yes of phenate Hot decantation Yes Yes Yes No No Yes NoWashing of No No Yes No No No No decanted organic phase Purification87.9 87.7 87.1 94.8 95.0 87.2 91.5 yield* (%) Residual PNCB <50 <50 <50180 <50 180 <50 ppm Total Cl ppm 40 18 <10 2800 2900 70 300 Chloridesppm 20 <10 <10 2700 2750 15 280 Total S ppm 30 40 15 26,000 25,000 4027,000 PNP OD 500 nm <0.1 <0.1 <0.1 >0.4 >0.4 0.1 >0.1*PNP/phenate taken

Example 4 Recycling of Mother Liquors and Washings from PNPCrystallization and Recycling of the PNP of the Aqueous Decantation andWashing Phases

The example is conducted according to Example 1, except that thecrystallization mother liquors and washings derived from thecrystallization of the PNP of Example 3 (F₃) are used to dilute thephenate crystallized before acidification: these liquors areconcentrated from 850 g to 400 g.

The solid, namely 12 g, which precipitates from the cooled aqueousdecantation (F₄) and washing (F₅) phases of Example 3, is recovered.

The precipitate is recycled to the point where the crystallized phenateis diluted.

134 g of dry solid, titrating as more than 99.5% PNP (0.959 moles), arerecovered.

The results obtained are as follows:

-   -   PNP yield relative to the phenate taken: 95.9%    -   residual PNCB ppm <50    -   total Cl ppm <10    -   total S ppm <50    -   PNP OD 500 nm <0.1

1-27. (canceled)
 28. A process for preparation of a nitrophenol from anitrohalobenzene comprising the steps of: (a) hydrolysis of anitrohalobenzene compound by reaction of the said compound with a base,(b) acidification to obtain the nitrophenol compound from its salt, byan acid treatment, (c) crystallization of the nitrophenol compoundobtained, (d) separation of the product obtained, said process furthercomprising at least the following steps: (e) concentration of thereaction medium after hydrolysis (a) and before acidific-ation (b), and(f) liquid/liquid decantation performed after acidification (b) andbefore crystalliz-ation (c) in order to remove the aqueous phaseobtained after acidification (b).
 29. The process according to claim 28,comprising the steps of hydrolysis of the nitrohalobenzene compound,concentration of the reaction medium, acidification, decantation,crystallization of the nitrophenol and separation.
 30. The processaccording to claim 28, comprising the steps of hydrolysis of thenitrohalobenzene compound, concentration of the reaction medium,crystallization of the nitrophenate, separation, acidification,decantation, crystallization of the nitrophenol and separation.
 31. Theprocess according to claim 28, comprising the steps of hydrolysis of thenitrohalobenzene compound, concentration of the reaction medium,optionally crystallization of the nitrophenate followed by separationthereof, acidification, decantation, washing of the organic phase,crystallization of the nitrophenol and separation.
 32. The processaccording to claim 28, wherein the basic hydrolysis of thenitrohalobenzene compound is performed by reacting it with an inorganicor organic base.
 33. The process according to claim 32, wherein thehydrolysis temperature lies between 100° C. and 200° C.
 34. The processaccording to claim 28, wherein the concentration of the reaction mediumis performed so as to increase the concentration of nitrophenol in themedium from 0.1% by weight to 10% by weight.
 35. The process accordingto claim 34, wherein the concentration is increased by decreasing thereaction pressure, by pressure release, while remaining in the aforesaidtemperature zone or by distilling under atmospheric pressure at atemperature of the order of 100° C., under a pressure slightly lowerthan atmospheric pressure selected so as to have a distillationtemperature lying between 80° C. and 99.6° C. or at a pressure greaterthan atmospheric pressure.
 36. The process according to claim 28,wherein the acidification is performed by addition of a protonic acid ofinorganic origin.
 37. The process according to claim 36, wherein thequantity of acid is at least equal to the quantity necessary forobtaining a pH lying between 1 and 7 at the end of acidification. 38.The process according to claim 36, wherein the reaction medium ismaintained at a temperature varying between 45° C. and 70°.
 39. Theprocess according to claim 28, wherein the crystallization of thenitrophenol is performed by cooling to a temperature which is atemperature lower than 40° C.
 40. The process according to claim 28,wherein the separation of the crystallized product is performed byfiltration or by centrifugation.
 41. The process according to claim 28,wherein a further operation of decantation of the two liquid phasesobtained is performed following the acidification, at a temperature of60-70° C.
 42. The process according to claim 30, wherein thecrystallization of the nitrophenate is performed at the end of theconcentration operation, by cooling to an ambient temperature and thatthe crystallized product is separated by filtration or centrifugation.43. The process according to claim 29, wherein a further step of waterwashing of the organic phase is interposed between the decantation andthe crystallization.
 44. The process according to claim 43, wherein themother liquors and washings from the crystallization of the nitrophenolare recycled to the hydrolysis of the nitrohalobenzene or to thedilution of the crystallized phenate after acidification.
 45. Theprocess according to claim 43, wherein at least part of the decantationliquors which result the acidification of the nitrophenate is recycledto the hydrolysis of the nitrohalobenzene or to the dilution of thecrystallized phenate after acidification.
 46. The process according toclaim 43, wherein the solid which precipitates to part of the cooleddecantation liquors is recycled to the hydrolysis of thenitrohalobenzene or to the dilution of the crystallized phenate afteracidification.
 47. The process according to claim 31, wherein theaqueous washings of the organic phase which decanted after acidificationof the nitrophenate are recycled to the hydrolysis of thenitrohalobenzene or to the dilution of the crystallized phenate afteracidification.
 48. The process according to claim 28, wherein thenitrohalobenzene corresponds to the formula:

wherein: X represents a fluorine, chlorine, bromine or iodine atom, theNO₂ group is in the ortho, meta or para position.
 49. The processaccording to claim 48, wherein the nitrohalobenzene corresponding to theformula (I) bears one or several other halogen atom(s) or one or severalnitro group(s) or one or several alkyl group(s) having from 1 to 4carbon atoms.
 50. The process according to claim 48, wherein thenitrohalobenzene is p-nitro-chlorobenzene.
 51. A Nitrophenol having: anitrohalobenzene content less than 180 ppm, and a halogen ions contentless than 40 ppm.
 52. The nitrophenol according to claim 24, having asulfur content lower than 200 ppm.
 53. A p-Nitrophenol having: ap-nitrohalobenzene content less than 180 ppm, and a halogen ions contentless than 40 ppm.
 54. The p-Nitrophenol according to claim 53, whereinit has a sulfur content preferably lower than 200 ppm, and still morepreferably lower 100 ppm.